Thermal method and apparatus

ABSTRACT

A thermal method for studying chemical responses, such as catalyzed polymerization reactions that includes the following three steps. The first step is to flow a chemical substance through a conduit, the conduit being in thermal communication with an electrical conductor, the electrical conductor being co-linear with the conduit, the electrical resistance of the electrical conductor being a function of the temperature of the electrical conductor. A length of stainless steel tubing can be used as both the conduit and the conductor. The second step is to flow electricity through the electrical conductor during the first step. The third step is to measure the electrical resistance of the electrical conductor during the second step to determine any change in the temperature of the conduit caused by a response of the chemical substance. An apparatus for studying chemical reactions that includes: a first conduit, the first conduit being an electrical conductor, the first conduit having a first end and a second end, the electrical resistance of the first conduit being a function of the temperature of the first conduit; a source of electricity, the source of electricity in electrical communication with the first conduit so that electricity can be flowed through the first conduit; a volt meter in electrical communication with the first conduit so that the voltage measured by the volt meter is an indication of the temperature of the first conduit.

This application claims the benefit of provisional application No.60/142,486 filed Jul. 6, 1999.

BACKGROUND OF THE INVENTION

Thermal methods and apparatus are known for studying chemical responses,such as phase changes or chemical reactions, by flowing a chemicalsubstance through a conduit and measuring a temperature change caused bythe response. For example, the conduit can be a covered channel in aplate, the channel being heated to a temperature at which a reactionwill occur by a plurality of electrical resistance heaters positionedalong the channel while a temperature change caused by a reaction ismeasured by a plurality of thermopiles which are also positioned alongthe channel (Zieren et al., American Institute of Chemical Engineers2^(nd) International Conference on Microreaction Technology (1998),Topical Conference Preprints, pages 154-163). Such systems represent aninteresting advance in the art but such systems are relatively complexand expensive to manufacture.

SUMMARY OF THE INVENTION

The instant invention provides a solution to the above-mentionedproblems. The instant invention is a thermal method for studyingchemical responses, comprising the steps of: (a) flowing a chemicalsubstance through a conduit, the conduit being in thermal communicationwith an electrical conductor, the electrical conductor being co-linearwith the conduit, the electrical resistance of the electrical conductorbeing a function of the temperature of the electrical conductor; (b)flowing electricity through the electrical conductor during step (a);and (c) measuring the electrical resistance of the electrical conductorduring step (b) to determine any change in the temperature of theconduit caused by a response of the chemical substance.

The instant invention is also an apparatus for studying chemicalreactions, comprising: a first conduit, the first conduit being anelectrical conductor, the first conduit having a first end and a secondend, the electrical resistance of the first conduit being a function ofthe temperature of the first conduit; a source of electricity, thesource of electricity in electrical communication with the first conduitso that electricity can be flowed through the first conduit; a voltmeter in electrical communication with the first conduit so that thevoltage measured by the volt meter is an indication of the temperatureof the first conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a specific apparatus embodiment of theinstant invention incorporating a coiled tube assembly and a pressureregulator;

FIG. 2 is a schematic drawing of the coiled tube assembly in greaterdetail;

FIG. 3 is a side view, part in full and part in cross-section, of thepressure regulator; and

FIG. 4 is a plot of temperature versus time using the instant inventionto study a catalyzed polymerization reaction.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, therein is shown a schematic drawing of aspecific apparatus embodiment 10 of the instant invention. The apparatusembodiment 10 includes a reservoir 11 filled with petroleum naphtha 12of a grade suitable for catalytically polymerizing ethylene dissolved inthe naphtha to polyethylene. A tube 13 conducts naphtha 12 to a HighPerformance Liquid Chromatography (HPLC) pump 14 set to pump the naphtha12 at a rate of two milliliters per minute. The pump 14 pumps naphtha 12to tubing coils 19, 20 and 21 by way of tubing 15, 16, 17 and 18.

A 0.5 micrometer HPLC in-line filter, not shown, is positioned in thetubing 15 to filter the naphtha from the pump 14. The tubing coils 19and 20 are each 52 feet (16 meters) long, {fraction (1/16)} inch (1.59millimeter) outside diameter, 0.004 inch (0.10 millimeter) insidediameter stainless steel tubing. The tubing coil 21 is 10 feet (3meters) long, {fraction (1/16)} inch (1.59 millimeter) outside diameter,0.010 inch (0.254 millimeter) inside diameter stainless steel tubing.Tubing 22 conducts naphtha 12 to HPLC injection valve 33.

The valve 33 has a twenty microliter injection loop, not shown, which isfilled using syringe 31. Tubing 23 conducts naphtha 12 to HPLC injectionvalve 34. The valve 34 has a twenty microliter injection loop, notshown, which is filled using syringe 32. The valves 33 and 34 areautomatically actuated using a general-purpose digital computer, notshown. An HPLC autosampler can be used to supply samples to valves 33 or34 if desired. Tubing 35, 36 and 37 conducts naphtha to a length oftubing 38 that is not an electrical conductor (such as HPLC grade PEEKtubing). Tubing 24 conducts naphtha 12 to in-line mixer 28. Differencesbetween the inside diameters and lengths of the tubing coils 19, 20 and21 direct most of the flow of naphtha 12 from the pump 14 through thetubing coil 21.

A source 26 of ethylene gas 27 is introduced at a rate of about twentyfive cubic centimeters per minute STP into the naphtha flowing in tubing24 by way of tubing 25. The source 26 of ethylene gas 27 consists of acylinder of ethylene connected to a pressure regulator (GO ModelPR50-1A11C3K111, San Dimas, Calif., set to regulate at 44.2 atmospheresor 4.6 megapascals) connected to a mass flow controller (PorterInstrument Co. Model 201-APBSVBAA, Hatfield, Pa.) connected to a backpressure regulator (GO Model BP60-1A11IEK111, San Dimas, Calif., set toregulate at 40.8 atmospheres or 4.2 megapascals) connected to a checkvalve (Nupro Model SS-4C1-1/3). The mass flow controller is housed in athermal enclosure maintained at sixty degrees Celsius (however, theelectronic components of the mass flow controller are positioned outsideof the thermal enclosure because they will not operate at sixty degreesCelsius).

The ethylene gas 27 is mixed with and dissolved into the naphtha 12 inan in-line mixer 28 (Alletch Part Numbers 20141 and 20147, DeerfieldIll.) and then conducted by tubing 40 to pressure transducer 29(Validyne Model P55D 4-V-1-60-S-4-B, Northridge, Calif.). Tubing 41 thenconducts the naphtha and ethylene to a length of tubing 30 that is notan electrical conductor (such as HPLC grade PEEK tubing). A tubing coil43 is connected at one end to the tubing 30 and at the other end to thefirst end of first conduit 44.

The tubing coil 43 is fifty inches (1.3 meters) long, {fraction (1/16)}inch (1.59 millimeter) outside diameter, 0.050 inch (1.27 millimeters)inside diameter stainless steel tubing. The first conduit 44 is a coilof stainless steel tubing which is seventy inches long (1.8 meters),{fraction (1/16)} inch (1.59 millimeter) outside diameter and 0.050 1.27millimeters) inside diameter. The second end of the first conduit 44 isconnected to a length of tubing 47 that is not an electrical conductor(such as HPLC grade tubing made from TEFLON brand FEP polymer) viapressure regulator 45 and tubing 46.

As will be discussed below in greater detail, the tubing coil 43 and thefirst conduit 44 are enclosed in thermal insulation 42 while tube 39connects tubing 38 with tubing coil 43 and the first end of the firstconduit 44.

Referring now to FIG. 2, therein is shown a schematic drawing of thecoiled tube assembly 42, 43, 44 of FIG. 1 in greater detail. Theconnection of the tube 39, the tubing coil 43 and the first conduit 44is facilitated by a {fraction (1/16)} inch (1.59 millimeter) stainlesssteel tee 50. The tube 39 is a length of {fraction (1/32)} inch 0.79millimeters) outside diameter, 0.007 (0.178 millimeters) inside diameterstainless steel tubing which is adapted to the tee 50 by inserting thetube 39 through a three inch (75 millimeter) length, not shown, of{fraction (1/16)} inch (1.59 millimeter) outside diameter, 0.040 inch(1.02 millimeter) inside diameter stainless steel tubing attached to thetee 50. The tube 39 is inserted in the three inch (75 millimeter) lengthof stainless steel tubing so that upon insertion the end of the tube 39bottoms out in the tee 50 and then the tube 39 is withdrawn 0.5millimeter. The tube 39 is then tightened to the three inch (75millimeter) length of stainless steel tubing using a {fraction (1/16)}by {fraction (1/32)} inch (1.59 by 0.79 millimeter) stainless steeltubing union, not shown.

The tubing coil 43 and first conduit 44 are wound on a cylinder offoamed silicone rubber thermal insulation 52. A cover of foamed siliconerubber thermal insulation 51 is also used so that the tubing coil 43 andfirst conduit 44 are essentially surrounded by thermal insulation.

A source of electricity 53 (two Kepco Model ATE 36-15M DC power supplyunits having their positive terminals in common) is connected from thepositive common terminal to tee 50 by wire 55. A negative terminal ofthe source of electricity 53 is connected near one end of the tubingcoil 43 by wire 56. The other negative terminal of the source ofelectricity 53 is connected near the second end of the first conduit 44by wire 54.

A voltmeter 62 (Keithley Model 2000 six and one half digit multimeter,equipped with a twenty channel multiplexer, Cleveland, Ohio) isconnected to tee 50 by wire 63. The voltmeter 62 is also shown connectedto an intermediate position of the first conduit 44 by wire 60. Themultiplexer of the voltmeter 62 alternatively connects the volt meter 62to wires 57, 58, 59 or 61 as programmed via the general purpose digitalcomputer, not shown. Wires 54-61 are preferably connected to the tubingcoil 43 and first conduit 44 by silver soldering. The non-conductivetubing 30, 38 and 47 shown in FIG. 1 provides electrical isolation forthe system shown in FIG. 2.

Referring now to FIG. 3, therein is shown a side view, part in full andpart in cross-section, of the pressure regulator 45. The pressureregulator 45 comprises a stainless steel body 74 which is drilledthrough to provide flow passageways 75 and 76. Passageway 75 isconnected to tube 46 of FIG. 1. The body 74 is also machined toaccommodate an o-ring seal 73. A 127 micrometer thick disk 72 ofstainless steel is biased against the body 74 by solenoid 70 (TrombettaModel Q517, having a twenty four volt coil, Monomonee Falls, Wis.) byway of stainless steel ram 71.

The ram 71 in FIG. 3 is shown being broader where it contacts the disk72 than at the solenoid 70. However, it has recently been foundpreferable to make the ram 71 a straight cylinder from the solenoid 70to the disk 72, the such modified ram 71 extending through a washer, thewasher being bolted to the body 74 to press the peripheral portion ofthe disk 72 against the body 74 while the central portion of the disk 72is free to spring upwards against the modified ram 71.

The amount of current supplied to the solenoid 70 is determined byfeedback control using the general-purpose digital computer, not shown,and the signal from the pressure transducer 29. If the pressuretransducer 29 senses a higher or lower pressure than desired, then thefeedback system feeds less or more current respectively to the solenoid70 so that the hydraulic pressure in the coil of tubing 43 and the firstconduit 44 is controlled to be essentially constant at a pressure of 400pounds per square inch (2.8 megapascals).

The method of the instant invention can be used to study a chemicalresponse that produces a change in temperature. For example, the instantinvention can be used to study a phase change of a chemical, or anexothermic or endothermic chemical reaction involving a chemicalsubstance. The method of the instant invention comprises the followingthree steps. The first step is to flow a chemical substance through aconduit, the conduit being in thermal communication with an electricalconductor, the electrical conductor being co-linear with the conduit,the electrical resistance of the electrical conductor being a functionof the temperature of the electrical conductor.

Referring now to FIG. 2, the first conduit 44 is made of stainless steeltubing. Stainless steel tubing is both a conduit for fluids and anelectrical conductor. The electrical resistance of a given length ofstainless steel tubing of a given inside and outside diameter is afunction of the temperature of the tubing. As a general rule, theelectrical resistance of any electrical conductor of a given dimensionis a function of the temperature of the conductor.

The first conduit 44 is thus also the electrical conductor of the methodof the instant invention and they are obviously in thermalcommunication. However, it should be understood that other structurescan be used. For example, a fused silica capillary tube can be used asthe conduit, the fused silica capillary tube being coated (oralternatively lined with) a metal (or other electrical conductor) as theelectrical conductor. Or, a channel can be formed in a body as theconduit and a strip of metal can be placed in, on or in thermalcommunication with the channel as the electrical conductor. The term“thermal communication” means that the temperature change caused by theresponse of the chemical substance must be thermally conducted to theelectrical conductor.

The electrical conductor must be “co-linear” with the conduit. In thesystem shown in FIG. 2, the conduit and the electrical conductor are thesame structure and thus are clearly co-linear. However, electricalconductors placed across and in thermal communication with a channelformed in a body (see, Zieren et al. discussed above) are not co-linear.An electrical conductor of a serpentine, square wave or sine wave placedin thermal communication with a straight length of channel formed in abody are also not “co-linear” with such a channel. Thus, the term“co-linear” means that the electrical conductor and the conduit haveessentially parallel longitudinal axes along the conduit and theelectrical conductor.

The limitation that the conduit and the electrical conductor be“co-linear” does not mean that the conduit and the electrical conductormust be arranged along a continuous straight line. The conduit and theelectrical conductor may be coiled (as shown in FIG. 2) or otherwiseconfigured as long as they are “co-linear” with each other as definedabove.

The second step of the instant invention is to flow electricity throughthe electrical conductor during the first step. Referring now to FIG. 2,the electricity flows in the circuit from the source of electricity 53,through wire 55, through first conduit 44, through wire 54 back to thesource of electricity 53. The amount of electrical current flowedthrough the electrical conductor is generally (but not necessarily)sufficient to significantly increase the temperature of the conduitsince the response of the chemical substance is often studied atelevated temperatures. When it is desired to study chemical responses atelevated temperatures, then the system can be preheated by the use, forexample, of the coiled stainless steel tubing 43 shown in FIG. 2 whichtubing 43 is electrically heated by the source of electricity 53 by wayof the wires 56 and 55.

The third step is to measure the electrical resistance of the electricalconductor during the second step to determine any change in thetemperature of the conduit caused by a response of the chemicalsubstance. Referring now to FIGS. 1 and 2, if a polymerization catalyst(0.02 Molar in naphtha) is injected by injection valve 33 and a catalystactivator (0.02 Molar in naphtha) is injected at the same time byinjection valve 34, then the active catalyst will meet the preheatednaphtha and ethylene stream in the tee 50 and flow through the firstconduit 44 toward the pressure regulator 45.

Heat is produced when the ethylene polymerizes in the first conduit 44to produce polyethylene as a reaction product. The heat increases thetemperature of the first conduit 44. The electrical resistance of thefirst conduit 44 can be conveniently measured using the volt meter 62 tomeasure the voltages of wires 58-61, which voltages are a function ofthe temperatures of the respective portions of the first conduit 44.

The preheater section (tubing coil 43) is heated by a current of 3.113amperes. The reactor section (first conduit 44) is heated by a currentof 2.389 amperes. The naphtha and ethylene being flowed through thepreheater section are heated from ambient temperature to 178 degreesCelsius. The naphtha and ethylene mixture being flowed through theconduit 44 is heated from 178 degrees Celsius to 182 degrees Celsiuswhen no injection of catalyst and catalyst activator is made.

Referring now to FIG. 4, therein is shown a plot of temperature of thefirst conduit 44 between wires 59 and 60 versus time in seconds afterthe injection of the catalyst and the activator. The plot shown in FIG.4 indicates that the temperature of the first conduit 44 at firstincreases from a baseline temperature of 180 degrees Celsius at about100 seconds, reaches a maximum temperature of about 187 degrees Celsiusat about 190 seconds and then decreases to essentially the baselinetemperature of 180 degrees Celsius by 800 seconds to produce atemperature “peak”.

The temperature peak can be measured by any conventional peakmeasurement technique such as peak area or peak height. A larger peak isan indication that the catalyst system injected has a greater catalyticeffect on the polymerization of the ethylene to polyethylene. Thepressure regulator 45 helps to maintain a constant hydraulic pressure inthe conduit 44 despite the increase in viscosity in the conduit 44caused by the polymerization of the ethylene to polyethylene.

The above discussion is made with respect to a specific apparatus andmethod. Of course the scope of the instant invention is much broaderthan the above discussed specific apparatus and method. For example, thechemical substance can be continuously flowed into the conduit, thechemical substance can be any reactive chemical or mixture of chemicalssuch as a mixture of monomers and any fluid can be flowed through theconduit (gas, liquid, supercritical fluid, or a suspension of amaterial(s) therein).

When the first conduit is a metal tube, then there are a number offactors that need to be considered to optimize the sensitivity of theinstant invention. For example, the ratio of the cross-sectional area ofthe metal of the tube to the cross-sectional area of the channel definedby the tube is preferably less than ten. The system shown in FIG. 1 hassuch a ratio of about 0.56 because relatively thin wall tubing is used.When 0.02 inch (0.51 millimeter) inside diameter {fraction (1/16)} inch(1.59 millimeter) stainless steel tubing is used in the system shown inFIG. 1, then the ratio is about 8.8 and the sensitivity of the system isabout ten times lower.

When the first conduit and the electrical conductor are a metal tube,then it is preferable to use a metal such as stainless steel that has arelatively high resistivity. If a metal is used that has a relativelylow resistivity, then more current is needed to produce a given powerdissipation. Of course, the use of a thinner wall metal tube of anygiven outside diameter will increase such a voltage drop due to greaterelectrical resistance per unit of length.

The reaction product flowing from the first conduit can be furtheranalyzed by any number of chemical analysis techniques such as massspectroscopy, gas chromatography and liquid chromatography. If desired,a plurality of parallel conduit/electrical conductor systems can be usedto increase the number of chemical responses that can be studied in anygiven period of time.

The conduit and electrical conductor are preferably surrounded bythermal insulation. For example, they can even be housed in a vacuum.However, useful results can be obtained without such thermal insulation.For example, useful results can be obtained by moving a stream of airover the conduit and the electrical conductor.

In general, a person of ordinary skill in the art will appreciate themyriad of factors (such as the thermal conductivity, heat capacity anddimensions of the conduit) that will influence any particularapplication of the instant invention. The primary benefit of the instantinvention is that it can provide a less complex and more economicalmethod and apparatus for studying the thermal effects of chemicalresponses. Another benefit of the instant invention is that it uses arelatively small amount of the chemical(s) being studied.

What is claimed is:
 1. A thermal method for studying chemical responses,comprising the steps of: (a) flowing a chemical substance through aconduit, the conduit being an electrical conductor, the electricalresistance of the electrical conductor being a function of thetemperature of the electrical conductor; (b) flowing electricity throughthe electrical conductor during step (a); and (c) measuring theelectrical resistance of the electrical conductor during step (b) todetermine any change in the temperature of the conduit caused by aresponse of the chemical substance.
 2. The method of claim 1, whereinthe chemical substance is a chemical reactant, and the response of thechemical substance is a reaction of the chemical reactant to produce areaction product.
 3. The method of claim 2, wherein in step (a) thechemical reactant is dispersed in a liquid flowing through the conduit,wherein in step (b) the conduit is heated by the electricity, andwherein a preselected amount of a catalyst for the reaction isintroduced into the liquid so that in step (c) the temperature of theconduit at first increases from a baseline temperature and thendecreases to essentially the baseline temperature to produce a measuredtemperature peak.
 4. The method of claim 3, wherein the electricalresistance of the electrical conductor is measured at more than onelocation of the electrical conductor.
 5. The method of claim 3, whereinthe hydraulic pressure of the liquid flowing through the conduit iscontrolled.
 6. The method of claim 3, wherein the chemical reactantcomprises a monomer and the reaction product comprises a polymer.
 7. Themethod of claim 3, wherein the electrical resistance of the electricalconductor is measured at more than one location of the electricalconductor, wherein the hydraulic pressure of the liquid flowing throughthe conduit is controlled, wherein the chemical reactant comprises amonomer and wherein the reaction product comprises a polymer.